Preparation of alkali metal substituted aromatic hydrocarbons



United States Patent 3,206,518 PREPARATIDN 0F ALKALI METAL SUBSTITUTED AROMATIC HYDROCARBONS Paul Kobetz, Baton Rouge, La., assignor to Ethyl Corporation, New York, N.Y., a corporation of Virginia No Drawing. Filed Mar. 30, 1961, Ser. No. 99,336 5 Claims. (Cl. 260-665) This invention relates broadly to a process for the preparation of alkali metal aryl compounds. More particularly, this invention is concerned with a metalation process to produce the alkali metal alkaryl products.

In the past, several methods of metalating aromatic hydrocarbons have been disclosed. John F. Nobis et al. in Industrial and Engineering Chemistry, March 1954, vol. 40, No. 3, described a method of reacting dispersed sodium and chlorobenzene to obtain phenyl sodium which in turn was reacted with toluene to obtain benzyl sodium which could then be carboxylated to obtain phenyl acetic acid. The reaction steps were:

As can readily be seen this is a long expensive process requiring a multiplicity of steps and a great deal of time. Another method outlined by Chester E. Claff et al., entitled The Metalation of Toluene by Potassium and Sodium, appearing in Journal of Organic Chemistry, vol. 20, 1955, pages 440-442, involves the reaction of toluene, potassium and sodium oxide to obtain benzyl potassium. The equation was Clafi et al., in the article, stated that sodium was found to be totally ineffective in place of potassium in this metalation reaction. Furthermore, in the absence of the metallic oxide, sodium or potassium was found to give very poor results. Moreover, in order for this reaction to be effective it was necessary to obtain the proper kinds and definite proportions of solid reagents.

In sharp'contrast to the methods outlined above, a one-step metalation process would be the most straight forward and economical method for preparing alkali metal alkaryl compounds.

It is therefore an object of this invention to provide a process for metalating an aromatic hydrocarbon. It is a further object to provide a one-step method whereby metalation of the aromatic hydrocarbon is achieved. Other objects of this invention will be readily apparent from the subsequent disclosure.

The above and other objects of this invention are accomplished by a process for producing an alkali metal alkaryl compound comprising reacting an alkali metal with alkyl substituted aromatic hydrocarbon and a dialkyl Group IIB compound at a temperature suflicient to effect the metalation of the aromatic hydrocarbon.

The alkali metals used in this reaction as the metalating agent are the Group I-A metals of the Periodic Chart of the Elements, Fisher Scientific Company, 1959. The Group I-A metals include lithium, sodium, potassium, rubidium, cesium and francium. Francium is rarely employed since it is not economically attractive. The preferred alkali metals are sodium and potassium because of availability and reactivity. The most preferred alkali metal is sodium since itis readily available and relatively low in price.

The particle size of the reactants of this invention is not critical. However, the speed of the reaction will generally be enhanced if the particle size ranges below about 100 microns. Generally it is preferred that the particle size range below about 50 microns since best reaction speeds are achieved in this range.

The aromatic hydrocarbon reactant in this process can be any alkyl substituted aromatic hydrocarbon wherein the alkyl group contains up to 15 carbon atoms. The aromatic hydrocarbon may contain up to 6 alkyl groups on the aromatic ring. The aromatic portion of the reactant is preferably mononuclear. Typical examples of the alkyl substituted aromatic hydrocarbons used in this invention are butyl benzene, dibutyl benzene, propyl benzene, isopropyl benzene, octyl benzene, mesitylene, 1-methyl-3- ethyl benzene, 1-methyl-4-ethyl benzene, isocumene, metatertiary butyl toluene, amyl benzene, hexaethyl benzene, hexamethyl benzene, isohexyl benzene, pentadecyl benzene, tetradecyl benzene, dodecyl benzene, heptyl benzene, and the like.

The preferred alkyl substituted aromatic hydrocarbons are those in which each alkyl group contains up to 5 carbon atoms wherein the said aromatic hydrocarbon contains up to 2 alkyl groups on the ring. Typical examples of these preferred reactants are toluene, xylene, cumene, ethyl benzene, diethyl benzene, and the like.

The Group IIB metal of the dialkyl Group IIB metal reactant of this invention can be cadmium or zinc. It is preferred for economic reasons, however, that the metal portion of the compound be zinc.

The alkyl portion of the dialkyl Group IIB metal reactant of this invention can contain up to 10 carbon atoms in each alkyl group. It is preferred, however, for economic reasons that the alkyl groups contain up to 5 carbon atoms.

Typical examples of the dialkyl Group IIB metal compounds used in this invention are dimethyl zinc, dimethyl cadmium, dipropyl zinc, dibutyl cadmium, dipentyl zinc, dipentyl cadmium, dihexyl zinc, diheptyl zinc, dioctyl zinc, dinonyl zinc, didecyl zinc, methyl ethyl zinc, methyl ethyl cadmium, ethyl propyl zinc, propyl butyl zinc, butyl amyl zinc, and the like. Because of economics and ease of handling, diethyl zinc is the most preferred dialkyl zinc reactant.

The process of this invention is a quantitative reaction wherein 2 moles of alkali metal are reacted with 2 moles of an alkyl substituted aromatic hydrocarbon such as toluene and 1 mole of dialkyl Group IIB compound. This is not to be construed that these definite quantitative proportions of reactants must be used. Quite to the contrary, the amounts of the reactants employed can be varied over a wide range. For example, between about 1 to 5, or higher or lower, moles each of the alkali metal and alkyl aromatic hydrocarbon per mole of the dialkyl Group IIB compound can be employed. It is preferred, however, to maintain essentially the stoichiometric amounts of the reactants, i.e., essentially 2 moles of alkali metal and 2 moles of alkyl substituted aromatic hydrocarbon per mole of dialkyl Group IIB compound since better results are obtained.

The products obtained from the process of this invention are alkali metal substituted aromatic hydrocarbons where the alkali metal attaches to the alkyl chain which in turn is attached to the aromatic ring. Metalation can occur on any carbon atom in the alkyl chain, but generally occurs on the end carbon atom due to the specificity of this unique process. Typical examples of compounds produced by the process of this invention are benzyl sodium, xylyl disodium, xylyl dipotassium, 5- phenylamyl cesium, 4-phenylbutyl sodium, xylyl d-icesium, phenylethyl potassium, cumenyl disodium, and the like.

A typical embodiment of this invention is the process for producing benzyl sodium by reacting sodium, diethyl zinc, and toluene at a temperature ranging from about 40 C. to about C.

off. The reaction was complete in 45 minutes.

The following working examples more fully demonstrate this invention. In these examples all parts and percentages are by weight unless otherwise specified.

EXAMPLE I Preparation of benzyl s dium.Sodium (20 parts) was mixed with 90 parts toluene under a nitrogen blanket and heated to 100 C. for a period of 2 hours with gentle stirring to make sodium sand. The mixture was cooled to room temperature and 22.3 parts of diethyl zinc were added. The mixture was stirred while maintaining the temperature at 20 C. by external cooling. After 5 minutes red solids were formed and ethane gas was given The reaction was permitted to go to completion after which the red product was recovered from the solution by filtration and washed with hexane. The red product was identified by elemental analysis as benzyl sodium contaminated with some by-product zinc metal.

EXAMPLE II Preparation of benzyl sodium-A run was made using 4 parts sodium, 6 parts diethyl zinc and 174 parts toluene. The reactants were added to reactor and heated to the reflux temperature of the system (110 C.) for a period of 4 hours. The red product, benzyl sodium, was formed and ethane gas was evolved.

The reaction mixture containing benzyl sodium was reacted with an excess carbon dioxide by bubbling it through the mixture at atmospheric pressure and room temperature for 2 hours. The mixture was then hydrolyzed with water and hydrochloric acid. Phenyl acetic acid was precipitated out.

Equally good results are obtained when other alkali metals such as potassium or lithium are reacted with toluene in the presence of diethyl zinc as described in the above examples.

EXAMPLE III Preparation of phenyl ethyl potassium.-Potassium (39 parts) is mixed with 106 parts ethyl benzene and 52 parts dipropyl zinc in an atmospheric pot equipped with a high speed stirrer. The reaction mixture is covered with a nitrogen blanket and heated to the reflux temperature of the system (136 C.) for a period of 3 hours. During this period the react-ion mixture turns red and propane is evolved. In this manner, 2-phenylethy1 potassium is obtained.

The phenylethyl potassium is carbonated by the addition of carbon dioxide bubbled through the reaction mixture at atmospheric pressure and room'temperature for a period of 1 /2 hours. The mixture is then hydrolyzed with water and hydrochloric acid to obtain phenylpropanoic acid which is precipitated out.

EXAMPLE IV Preparation of xylyl dicesium.-Cesium (80 parts) is mixed with 50 parts p-xylene and 40 parts dibutyl cadmium in an atmospheric pot equipped with a high speed stirrer. The reaction mixture is covered with argon gas to prevent contact with air and the mixture is heated to the reflux temperature of the system (135140' C.) for a period of 5 hours. During this period solid products are formed and butane is evolved. The product obtained in high yield is xylyl dicesium.

Xylyl dicesium is carbonated by the addition of an excess carbon dioxide bubbled through the react-ion mixture at atmospheric pressure and room temperature for a period of 45 minutes. The mixture is then hydrolyzed by the addition of Water and hydrochloric acid to obtain p-xylene-a,a'-dicarboxylic acid in high yields.

EXAMPLE V Preparation of cumene 5,6 dis0dium.Sodium (23 parts) is mixed with 120 parts cumene and 100 parts diamyl cadmium and heated to the reflux temperature of 4 the system (153 C.) for a period of 1 hour. During the reaction, solids are formed and pentane gas is given off. The product cumene-B,/3'-disodium is obtained in high yield.

Cumenyl disodium is carbonated and hydrolyzed in the same manner as set forth in Example 1V to obtain cun1ene-[S',B-dicarboxylic acid in high yields.

Excellent results are also obtained when alkyl substituted aromatic hydrocarbons such as 1-methyl-3-ethyl benzene, m-tertiary benzene, and the like are reacted with sodium and a dialkyl zinc or cadmium compound according to the procedures of any of the above examples.

Temperatures employed in this reaction can be varied but generally range from about 40 C. to about 200 C. However, to prevent undesirable side reactions from occurring while still obtaining a reasonably fast reaction rate, it is preferred to employ temperatures ranging from about 50 C. to about C.

Solvents may be employed in this reaction but it is preferred that the alkyl substituted aromatic hydrocarbon be metalated without the use of a solvent. If solvents are employed, however, aliphatic hydrocarbons, inert ethers such as the glycol ethers, and the like may be used.

The reaction time for the metalation reaction ranges from about 10 minutes to about 8 hours although longer times can be employed if desired. The preferred reaction time, however, ranges from about 30 minutes to about 4 hours since best results are obtained.

In handling and reacting the alkali metal with the alkyl substituted aromatic hydrocarbon in the presence of a dialkyl Group IIB compound an inert atmosphere should be employed to prevent oxidation of the reaction mixture. Typical examples of the gases used to prevent reactants from coming in contact with air are nitrogen, argon, krypton, and the like.

As stated in the above examples, the products obtained in the process of this invention may be carbonated by the addition of carbon dioxide to the reaction mixture containing the metalated product. The carbonatation may be accomplished by the well known methods generally employed for the reaction of an alkali metal-carbon bond with carbon dioxide. This can be done at room temperature and higher if desired. The reaction mass may then be hydrolyzed by the addition of water and hydrochloric acid to form the carboxylic acid or other conventional techniques of hydr-olyzing salts to their corresponding acids.

The alkali metal alkaryl products of this invention are valuable chemical intermediates. They may be carboxylated as outlined hereinabove to obtain the carboxylic acid derivatives. These acid derivatives have many varied and valuable uses. For instance, phenyl acetic acid, which is obtained from benzyl sodium, a product of my invention, is used for making perfumes. The esters of these acids can be used as monomers for polymers. They also have uses as plasticizers and synthetic high temperature lubricants.

Having thus'described the process of this invention, it is not intended that it be limited except as set forth in the following claims.

What is claimed is:

1. A process of producing an alkali metal alkaryl compound comprising reacting an alkali metal with an alkyl substituted aromatic hydrocarbon and a dialkyl Group II-B metal compound wherein said Group II-B metal is selected from the group consisting of zinc and cadmium at a temperature sufiicient to effect metalation; said metalation occurring on the alkyl substituent of said alkyl substituted aromatic hydrocarbon.

2. The process of claim 1 wherein said alkali metal is sodium.

3. The process of claim 1 wherein said alkyl substituted aromatic hydrocarbon is toluene.

4. The process of claim 1 wherein said dialkyl Group II-B metal compound is diethyl zinc.

5. The process of producing benzyl sodium comprising The Chemistry of Organometallic Compounds, reacting sodium with toluene and diethyl zinc at the re- Rochow et a1., Wiley & Sons, Inc., New York, 1957, pp.

flux temperature of the system. 48-54, 103 and 104.

The Chemistry of Organometallic Compounds, References Cited by the Exammer 5 Rochow et aL, Wiley & Sons, Inc., New York, 1957, pp.

UNITED STATES PATENTS 48 and 54.

2,954,410 9/60 Frank et a1. 260665 TOBIAS E. LEVOW, Primary Examiner.

OTHER REFERENCES ALPHONSO D. SULLIVAN, MILTON STERMAN,

(1 3333 et a1.: Chemical Reviews, vol. 54, No. 5, p. 866 0 Examiners 

1. A PROCESS OF PRODUCING AN ALKALI METAL ALKARYL COMPOUND COMPRISING REACTING AN ALKALI METAL WITH AN ALKYL SUBSTITUTED AROMATIC HYDROCARBON AND A DIALKYL GROUP II-B METAL COMPOUND WHEREIN SAID GROUP II-B METAL IS SELECTED FROM THE GROUP CONSISTING OF ZINC AND CADMIUM AT A TEMPERATURE SUFFICIENT TO EFFECT METALATION; SAID METALATION OCCURING ON THE ALKYL SUBSTITUENT OF SAID ALKYL SUBSTITUTED AROMATIC HYDROCARBON. 